1. Field of the Invention
The present invention relates to machine tools for shaping a work piece, and more particularly to a system including a rotary cutter and associated cooperating cutting inserts.
2. Description of the Related Art
When machining a work piece utilizing rotary cutters provided with replaceable inserts, it is frequently desirable to impart a final finish in which marks such as discernible ridges due to machining have been eliminated. Such marks may not be objectionable in rough or coarse machining, but are objectionable in fine finishing work. These marks are produced incidentally in machining operations, and result from the relation of cutting edges of the inserts to the work piece. In most cutters such as end mills, tool design emphasizes efficiency and productivity, with little regard for fineness of finish of a machined work piece.
Nonetheless, the machine tool industry has appreciated that steps such as eliminating machining steps or operations provides economic benefits. One such area which may be improved is that of eliminating overlap marks. Illustratively, U.S. Pat. No. 5,944,456, issued to Shirley et al. on Aug. 31, 1999, and of common ownership with the present invention, shows an end mill type cutter having staggered, overlapping inserts having radiused corners. Peak shaving of the work piece results in improved finishing characteristics as regards undesirably high peaks or ridges, which would otherwise detract from the finished appearance.
However, it is possible for end mill cutters to suffer from leaving lap lines due to carving out valleys or inwardly projecting marks in the work piece, as well as carving out peaks. This may arise due to variations in manufacturing tolerances, which variations may for example cause inserts to display radial runout, or project to unintended degrees from the hypothetical cylindrical envelope or outer surface of a rotary cutter. Radial runout is defined as the variation in the radius between a cylinder or circle and a perfectly uniform or straight cylinder configuration or circle. Runout is apt to gouge out unintended valleys which appear as undesirable conspicuous lap lines. Overlapped, staggered inserts in and of themselves cannot overcome such detractions to otherwise superlative finishes, as staggering can reduce peaks but cannot compensate for overly deep valleys. This situation is depicted in FIG. 4, wherein a representative work piece 2 has ideal upper and lower facets 4, which would result from perfect alignment of cutting inserts (not shown) having flat cutting edges, and one misaligned facet 6, which could result from an insert (not shown) which is misaligned due to radial runout of its associated pocket. In the situation illustrated, the degree or magnitude of radial runout does not exceed the manufacturing tolerances.
It will clearly be seen that an overlap mark 8 exists where the insert which cut facet 6 passed over work piece 2. This overlap mark 8 is highly conspicuous, and mars what would otherwise be an acceptable finish. There remains a need in the art for a rotary cutter which can control both excessive peaks and also excessive valleys formed in machined surfaces.